Method of monitoring the status of a wound

The present application is a continuation of non-provisional U.S. patent application Ser. No. 15/726,399, filed on Oct. 6, 2017, which is a continuation of non-provisional U.S. patent application Ser. No. 14/876,535, filed on Oct. 6, 2015. U.S. patent application Ser. No. 14/876,535 claims priority to provisional U.S. patent application No. 62/060,322, filed on Oct. 6, 2014; is a continuation-in-part of non-provisional U.S. patent application Ser. No. 13/439,177, filed on Apr. 4, 2012 (now U.S. Pat. No. 10,169,860), which claims priority to provisional U.S. patent application No. 61/516,459, filed on Apr. 4, 2011; and is a continuation-in-part of non-provisional U.S. patent application Ser. No. 14/577,571, filed on Dec. 19, 2014, which claims priority to provisional U.S. patent application No. 61/921,717, filed on Dec. 30, 2013, and to non-provisional U.S. patent application Ser. No. 13/439,177.

The present invention relates generally to methods of using non-invasive technologies in medical care. More specifically, the present invention relates to novel thermal imaging methods and the use of the same in the medical field.

Over the last century, clinicians, which term includes herein certified and licensed medical doctors of all specialties, osteopathic doctors of all specialties, podiatrists, dental doctors of all specialties, chiropractors, veterinarians of all specialties, nurses, and medical imaging technicians, have become dependent on the use of medical devices that assist them in their delivery of patient-centered care. The common function of these devices is to assist and not replace the clinical judgment of the clinician. This fulfills the dictum that best practice is clinical judgment assisted by scientific data and information.

Entering into the era of computer science and sophisticated electronics, clinicians have the opportunity to be supported by data and information in a statistically significant and timely fashion. These advancements have allowed more extensive and useful collection of meaningful data that can be acquired, analyzed, and applied in conjunction with the knowledge and expertise of the clinician.

Medical long-wave infrared (LIR) thermography has been known to be beneficial in the evaluation of thermal heat intensity and gradiency relating to abnormalities of the skin and underlying tissue (SUT). Although this technology has expanded to other areas of medical evaluation, the scope of this patent application is limited to the skin and underlying tissue abnormalities. These abnormalities include the formation of deep tissue injury (DTI) and subsequent necrosis caused by mechanical stress, infection, auto-immune condition, and vascular flow problems. DTI caused by mechanical stress (pressure, shear and frictional forces) can be separated into three categories. The first category is a high magnitude/short duration mechanical stress represented by traumatic and surgical wound and/or areas of interest. The second category is low magnitude/long duration mechanical stress represented by pressure ulcer development, which is also a factor in the development of ischemic and neuropathic wound and/or areas of interests. The third category is a combination of categories one and two represented by pressure ulcer formation in the bariatric patient.

The pathophysiologic conditions that occur with DTI and subsequent necrosis of the affected tissue are ischemia, cell distortion, impaired lymphatic drainage, impaired interstitial fluid flow, and reperfusion injury: Category one is dominated by cell distortion and even destruction. Category two is dominated by ischemia. Category three is a combination of cell distortion and ischemia.

Hypoxia causes aerobic metabolism to convert to anaerobic metabolism. This occurrence causes lactic acidosis followed by cell destruction, release of enzymes and lytic reactions. The release of these substances causes additional cell injury and destruction, and initiation of the inflammatory response.

It is very important to recognize that ischemic-reperfusion injury is associated with all of the above mechanical stress induced underlying tissue injuries. This condition is caused by a hypoxia induced enzymatic change and the respiratory burst associated with phagocytosis when oxygen returns after an ischemic event. The result of ischemic-reperfusion injury is the formation of oxygen free radicals (hydroxyl, superoxide, and hydrogen peroxide) that cause damage to healthy and already injured cells leading to extension of the original injury

Underlying tissue injury and subsequent necrosis can also be caused by vascular disorders. Hypoxia can be caused by an arterial occlusion or by venous hypertension. Lymphatic flow or node obstruction can also create vascular induced injury by creating fibrous restriction to venous drainage and subsequent cellular stasis in the capillary system. These disorders are also accentuated by reperfusion injury and oxygen free radical formation.

Infection of the skin (impetigo), underlying tissue (cellulitis), deep tissue (fasciitis), bone (osteomyelitis) and cartilage (chondritis) causes injury and necrosis of the affected tissue. Cells can be injured or destroyed by the microorganism directly, by toxins released by the microorganism and/or the subsequent immune and inflammatory response. These disorders are also accentuated by reperfusion injury and oxygen free radical formation.

Auto-immune morbidities of the skeletal joints (rheumatoid arthritis), skin and underlying tissue (tendonitis, myelitis, dermatitis) and blood vessels (vasculitis) cause similar dysfunction and necrosis of the tissue being affected by the hypersensitivity reactions on the targeted cells and the subsequent inflammatory response. Again, these conditions are accentuated by reperfusion and oxygen free radical formation.

The common event that addresses all of the above skin and underlying tissue injuries is the inflammatory response. This response has two stages. The first stage is vascular and the second is cellular. The initial vascular response is vasoconstriction that will last a short time. The constriction causes decrease blood flow to the area of injury. The decrease in blood flow causes vascular “pooling” of blood (passive congestion) in the proximal arterial vasculature in the region of injury and intravascular cellular stasis occurs along with coagulation.

The second vascular response is extensive vasodilation of the blood vessels in the area of necrosis. This dilation along with the “pooled” proximal blood causes increased blood flow with high perfusion pressure into the area of injury. This high pressure flow can cause damage to endothelial cells. Leakage of plasma, protein, and intravascular cells causes more cellular stasis in the capillaries (micro-thrombotic event) and hemorrhage into the area of injury. When the perivascular collagen is injured, intravascular and extravascular coagulation occurs. The rupture of the mast cells causes release of histamine that increases the vascular dilation and the size of the junctions between the endothelial cells. This is the beginning of the cellular phase. More serum and cells (mainly neutrophils) enter into the area of the mixture of injured and destroyed cells by the mechanism of marginalization, emigration (diapedesis) and the chemotaxic recruitment (chemotaxic gradiency). Stalling of the inflammatory stage can cause the area of necrosis (ring of ischemia) to remain in the inflammatory stage long past the anticipated time of 2-4 days. This continuation of the inflammatory stage leads to delayed resolution of the ischemic necrotic event.

The proliferation stage starts before the inflammatory stage recedes. In this stage angiogenesis occurs along with formation of granulation and collagen deposition. Contraction occurs, and peaks, at 5-15 days post injury.

Re-epithelialization occurs by various processes depending on the depth of injury. Partial thickness wound and/or area of interests can resurface within a few days. Full thickness wound and/or area of interests need granulation tissue to form the base for re-epithelialization to occur. The full thickness wound and/or area of interest does not heal by regeneration due to the need for scar tissue to repair the wound and/or area of interest. The repaired scarred wound and/or area of interest has less vascularity and tensile strength of normal regional uninjured skin and underlying tissue. The final stage is remodeling. In this stage the collagen changes from type III to a stronger type I and is rearranged into an organized tissue.

All stages of wound and/or area of interest healing require adequate vascularization to prevent ischemia, deliver nutrients, and remove metabolic waste. Following the vascular flow and metabolic activity of a necrotic area is currently monitored by patient assessment and clinical findings of swelling, pain, redness, increased temperature, and loss of function.

Medical devices are now available to assist the clinician in defining the presence, type, and status of the skin and underlying tissue injury. The LIR thermal and digital imaging device is a non-contact and non-radiating device that can be utilized bedside. The combination of imagers allows both visible and invisible radiation from the body to be evaluated. (See.) This allows both the anatomical and physiologic status of the skin and underlying tissue to be evaluated for injuries or disorders that are not yet clinically recognizable. By visualizing the IR thermal intensity, the clinician can evaluate the gradiency of the long-wave radiation emitted from the body region being imaged. The ability to visualize the thermal gradiency allows the clinician to evaluate the metabolic activity and blood flow of the region being imaged. The normal underlying tissue can be used as a control for that specific imaging procedure.

Having a real time control allows an area of interest (AOI) to be recognized. The AOI can be of greater intensity (hotter) or less intensity (cooler) than the normal underlying tissue of that region of the body. The AOI can then be evaluated by the clinician for the degree of metabolism, blood flow, necrosis, inflammation and the presence of infection by comparing the warmer or cooler thermal intensity of the AOI or wound and/or area of interest base and peri-AOI or wound and/or area of interest area to the normal underlying tissue of the location being imaged. Serial imaging also can assist the clinician in the ability to recognize improvement or regression of the AOI or wound and/or area of interest over time.

The use of an LIR thermal and digital visual imager can be a useful adjunct tool for clinicians with appropriate training to be able to recognize physiologic and anatomical changes in an AOI before it presents clinically and also the status of the AOI/wound and/or area of interest in a trending format. By combining the knowledge obtained from the images with a comprehensive assessment, skin and underlying tissue evaluation, and an AOI or wound and/or area of interest evaluation will assist the clinician in analyzing the etiology, improvement or deterioration, and the presence of infection affecting the AOI or wound and/or area of interest.

The foundational scientific principles behind LIR thermography technology are energy, heat, temperature, and metabolism.

Energy is not a stand-alone concept. Energy can be passed from one system to another, and can change from one form to another, but can never be lost. This is the First Law of Thermodynamics. Energy is an attribute of matter and electromagnetic radiation. It is observed and/or measured only indirectly through effects on matter that acquires, loses or possesses it and it comes in many forms such as mechanical, chemical, electrical, radiation (light), and thermal.

The present application focuses on thermal and chemical energy. Thermal energy is the sum of all of the microscopic scale randomized kinetic energy within a body, which is mostly kinetic energy. Chemical energy is the energy of electrons in the force field created by two or more nuclei, mostly potential energy.

Energy is transferred by the process of heat. Heat is a process in which thermal energy enters or leaves a body as the result of a temperature difference. Heat is therefore the transfer of energy due to a difference in temperature, heat is a process and only exists when it is flowing. When there is a temperature difference between two objects or two areas within the same object, heat transfer occurs. Heat energy transfers from the warmer areas to the cooler areas until thermal equilibrium is reached. This is the Second Law of Thermodynamics. There are four modes of heat transfer: evaporation, radiation, conduction and convection.

Molecules are the workhorses and are both vehicles for storing and transporting energy and the means of converting it from one form to another. When the formation, breaking, or rearrangement of the chemical bonds within the molecules is accompanied by the uptake or release of energy it is usually in the form of heat. Work is completely convertible to heat and defined as a transfer due to a difference in temperature, however work is the transfer of energy by any process other than heat. In other words, performance of work involves a transformation of energy.

Temperature measures the average randomized motion of molecules (kinetic energy) in a body. Temperature is an intensive property by which thermal energy manifests itself. It is measured by observing its effect on some temperature dependent variable on matter (i.e. ice/steam points of water). Scales are needed to express temperature numerically and are marked off in uniform increments (degrees).

As a body loses or gains heat, its temperature changes in direct proportion to the amount of thermal energy transferred from a high temperature object to a lower temperature object. Skin temperature rises and falls with the temperature of the surroundings. This is the temperature that is referred to in reference to the skins ability to lose heat its surroundings.

The temperature of the deep tissues of the body (core temperatures) remains constant (within±1° F./±0.6° C.) unless the person develops a febrile illness. No single temperature can be considered normal. Temperature measurements on people who had no illness have shown a range of normal temperatures. The average core temperature is generally considered to be between 98.0° F. and 98.6° F. measured orally or 99.0° F. and 99.6° F. measured rectally. The body can temporarily tolerate a temperature as high as 101° F. to 104° F. (38.6° C. to 40° C.) and as low as 96° F. (35.5° C.) or lower.

Metabolism simply means all of the chemical reactions in all of the cells of the body. Metabolism creates thermal energy. The metabolic rate is expressed in terms to the rate of heat release during the chemical reactions. Essentially all the energy expended by the body is eventually converted into heat.

Since heat flows from hot to cold temperature and the body needs to maintain a core temperature of 37.0° C.±0.75° C., the heat is conserved or dissipated to the surroundings. The core heat is moved to the body surface by blood flow. Decreased flow to the body surface helps conserve heat, while increased flow promotes dissipation. Conduction of the core heat to the body surface is fast, but inadequate alone to maintain the core temperature. Heat dissipation from the body surface (3 mm microclimate) also occurs due to the conduction, convection and evaporation.

Heat production is the principal by-product of metabolism. The rate of heat production is called the metabolic rate of the body. The important factors that affect the metabolic rate are:

Most of the heat produced in the body is generated in the deep organs (liver, brain, heart and the skeletal muscles during exercise). The heat is then transferred to the skin where the heat is lost to the air and other structures. The rate that heat is lost is determined by how fast heat can be conducted from where it is produced in the body core to the skin.

The skin, underlying tissues and especially adipose tissue are the heat insulators for the body. The adipose tissue is important since it conducts heat only 33% as effective as other tissue and specifically 52% as effective as muscle. Conduction rate of heat in human tissue is 18 kcal/cm/m2k. The skin and underlying tissue insulator system allows the core temperature to be maintained yet allowing the temperature of the skin to approach the temperature of the surroundings.

Blood flows to the skin from the body core in the following manner. Blood vessels penetrate the adipose tissue and enter a vascular network immediately below the skin. This is where the venous plexus comes into play. The venous plexus is especially important because it is supplied by inflow from the skin capillaries and in certain exposed areas of the body (hands-feet-ears) by the highly muscular arterio-venous anastomosis. Blood flow can vary in the venous plexus from barely above zero to 30% of the total cardiac output. There is an approximate eightfold increase in heat conductance between the fully vasoconstricted state and the fully vasodilated state. The skin is an effective controlled heat radiator system and the controlled flow of blood to the skin is the body's most effective mechanism of heat transfer from the core to the surface.

Heat exchange is based on the scientific principle that heat flows from warmer to cooler temperatures. Temperature is thought of as heat intensity of an object. The methods of heat exchange are: radiation (60%), loss of heat in the form of LIR waves (thermal energy), conduction to a solid object (3%), transfer of heat between objects in direct contact and loss of heat by conduction to air (15%) caused by the transfer of heat, caused by the kinetic energy of molecular motion. Much of this motion can be transferred to the air if it is cooler than the surface. This process is self-limited unless the air moves away from the body. If that happens, there is a loss of heat by convection. Convection is caused by air currents. A small amount of convection always occurs due to warmer air rising. The process of convection is enhanced by any process that moves air more rapidly across the body surface (forced convection). This includes fans, air flow beds and air warming blankets.

Convection can also be caused by a loss of heat by evaporation which is a necessary mechanism at very high air temperatures. Heat (thermal energy) can be lost by radiation and conduction to the surroundings as long as the skin is hotter than the surroundings. When the surrounding temperature is higher than the skin temperature, the body gains heat by both radiation and conduction. Under these hot surrounding conditions, the only way the body can release heat is by evaporation. Evaporation occurs when the water molecule absorbs enough heat to change to gas. Due to the fact water molecules absorb a large amount of heat in order to change into a gas, large amounts of body heat can be removed from the body.

Insensible heat loss dissipates the body's heat and is not subject to body temperature control (water loss through the lungs, mouth and skin). This accounts for 10% heat loss produced by the body's basal heat production. Sensible heat loss by evaporation occurs when the body temperature rises and sweating occurs. Sweating increases the amount of water to the skins surface for vaporization. Sensible heat loss can exceed insensible heat loss by 30 times. The sweating is caused by electrical or excess heat stimulation of the anterior hypothalamus pre-optic area.

The role of the hypothalamus (anterior pre-optic area) in the regulation of the body's temperatures occurs due to nervous feedback mechanisms that determine when the body temperature is either too hot or too cold.

The role of temperature receptors in the skin and deep body tissues relate to cold and warm sensors in the skin. Cold sensors outnumber warm sensorsto. The deep tissue receptors occur mainly in the spinal cord, abdominal viscera and both in and around the great veins. The deep receptors mainly detect cold rather than warmth. These receptors function to prevent low body temperature. These receptors contribute to body thermoregulation through the bilateral posterior hypothalamus area. This is where the signals from the pre-optic area and the skin and deep tissue sensors are combined to control the heat producing and heat conserving reactions of the body.

“Temperature Decreasing Mechanisms” include:

“Temperature Increasing Mechanisms” include:

LIR thermography evaluates the infra-red thermal intensity. The microbolometer is a 320×240 pixel array sensor that can acquire the long-wave infrared wavelength (7-14 micron) (NOT near-infrared thermography) and convert the thermal intensity into electrical resistance. The resistance is measured and processed into digital values between 1-254. A digital value represents the long-wave infrared thermal intensity for each of the 76,800 pixels. A grayscale tone is then assigned to the 1-254 thermal intensity digital values. This allows a grayscale image to be developed.

Using LIR thermography is a beneficial device to monitor metabolism and blood flow in a non-invasive test that can be performed bedside with minimal patient and ambient surrounding preparation. The ability to accurately measure the LIR thermal intensity of the human body is made possible because of the skin's emissivity (0.98±is 0.01), which is independent of pigmentation, absorptivity (0.98±0.01) reflectivity (0.02) and transmitability (0.000). The human skin mimics the “blackbody” radiation concept. A perfect blackbody only exists in theory and is an object that absorbs and reemits all of its energy. Human skin is nearly a perfect blackbody as it has an emissivity of 0.98, regardless of actual skin color. These same properties allow temperature degrees to be assigned to the pixel digital value. This is accomplished by calibration utilizing a “blackbody” simulator and an algorithm to account for the above factors plus ambient temperatures. A multi-color palate can be developed by clustering pixel values. There are no industry standards how this should be done so many color presentations are being used by various manufacturers. The use of gray tone values is standardized, consistent and reproducible. Black is usually considered cold and white is usually considered hot by the industry.

An LIR camera has the ability to detect and display the LIR wavelength in the electromagnetic spectrum. The basis for infrared imaging technology is that any object whose temperature is above 0° K radiates infrared energy. Even very cold objects radiate some infrared energy. Even though the object might be absorbing thermal energy to warm itself, it will still emit some infrared energy that is detectable by sensors. The amount of radiated energy is a function of the object's temperature and its relative efficiency of thermal radiation, known as emissivity.

Emissivity is a measure of a surface's efficiency in transferring infrared energy. It is the ratio of thermal energy emitted by a surface to the energy emitted by a perfect blackbody at the same temperature.

LIR thermography is a beneficial device to monitor metabolism, and blood flow, and profusion of the skin and underlying tissue in a non-invasive test that can be performed bedside with minimal patient and ambient surrounding preparation. It uses the scientific principles of energy, heat, temperature and metabolism. Through measurement and interpretation of thermal energy, it produces images that will assist clinicians to make a significant impact on wound and/or area of interest care (prevention, early intervention and treatment) through detection.

Accurate and repeatable measurement of size is essential for documenting progression or regression of the wound and/or area of interest. The long-accepted gold standard of length times width wound and/or area of interest measurement has been shown to have significant errors between when used to compare the results of one observer to another. The first part of the present invention provides a system and method of tracing the wound and/or area of interest edge on a visual image to provide clinicians with both measurements of area and perimeter but the area and perimeter measurement have been shown to be more accurate than length times width with the perimeter measurement being the most accurate. Another aspect of the present invention discloses a system and method for using long wave infrared thermography to analyze physiological aspects such as perfusion and metabolic activity as measured by the effect of a body surface temperature. In another aspect of the present invention there is disclosed a new combination of digital and long wave infrared thermography cameras to simultaneously capture a visual and infrared image of a wound and/or area of interest and surrounding body surface.

Once captured the visual image is used to document the appearance of a wound and/or area of interest, trace the wound and/or area of interests edge, and determine the area and perimeter of the wound and/or area of interest. The long wave infrared thermographic camera however is used to provide insight into the physiological functions of a wound and/or area of interest and surrounding body surface. The present invention provides means for a trace visual image's wound and/or area of interest to be overlaid onto the congruent thermal wound and/or area of interest shown by the long wave infrared thermographic camera.

The present invention uses long wave infrared thermography as a temperature measurement technique for the visualization and quantification of thermal energy emitted by the human body surface. When using long wave infrared thermography, thermal energy is represented through a unique conversion of gray scale pixel values to temperature values. The gray scale pixel value is a spectrum of absolute white to absolute black where pixel value of one (absolute black) is usually (but not necessarily) the coolest and a pixel value of 254 (absolute white) is usually (but not necessarily) the warmest.

Advantageously the system and methods of the present invention do not provide absolute measurements of temperatures. Instead, the system and method of the present invention allows clinicians to measure and record the temperature of a wound and/or area of interest area of interest and compare that to known unaffected areas on the patient. Thus, the effects of extrinsic and intrinsic variables that affect absolute temperature on a given day and make absolute measurements unreliable for clinical purposes, especially when taken across different days or by different clinicians, are avoided. Some of these intrinsic variables include the normal cycle of thermal production, age, chromatic morbidities, body region, medications, core temperature and others. Extrinsic variables including ambient temperature, humidity, air convection, climate adaption of the tissue, configuration of the body surface, sub straight temperature of the infrared core.

When assessing temperature data from multiple points in time, it is essential that the intrinsic and extrinsic variables described above are minimized. To accomplish this, selection of an unaffected area on a body surface can be used as a control relative to an affected area or likely affected area such as a wound and/or area of interest area of interest. Because the control is exposed to the same intrinsic and extrinsic variables as the affected area, a comparison of the two makes them independent of such variables. Since the temperature data can vary between body regions, it is preferable that the selection of the control area occur on or near the same body surface of the area of interest. If unable to obtain the above, compare to same area on the contralateral side of the body or an available part of the body of the contralateral side is not available. This new reference area should be reproducible for a particular patent.